The Restoration of Old Prints and Engravings

Manufacturer and builder 7, 1869

This process, discovered by Professor Gorup-Basanez, of Erlangen, Germany, is based upon the application of ozone. Old prints, wood-cuts, and copper engravings, which have become dark brown by age, or painted over, or by any means soiled, may by its use be restored and made as white as if they had just left the press. The print itself is thereby not in the least changed. Gorup-Besanez obtained it book which was published in the sixteenth century, and in which some pages were besmeared with a glossy black pigment, so that they were perfectly illegible. Indeed, the marks were similar to the censor-strokes of a Russian gazette. If our printing ink had been used by the monks of the sixteenth century, any attempts to remove it would most certainly have been in vain. However, on treating the book with ozone for thirty-six hours, the color disappeared entirely, so that the most careful observer would not have been able to detect the least trace of the marks referred to. A wood engraving of Dürer, which had been painted over with a dark yellow pigment, was also perfectly restored. The process in question is so easy that any person, with a little experience in experimental chemistry, may convince himself of its efficiency. The professor even makes use of it as an experimental demonstration in his lectures on ozone. Ink is so perfectly removed by ozone that the paper appears as if it had never been profaned by the pen, and it acts more quickly than chlorine. The paper which has been thus cleaned must afterward be drawn through water acidulated with a few drops of muriatic acid, in order that the iron of the ink, which is left behind, may also be removed. Printing ink is not attacked by ozone unless after a considerable time. Oily spots or stains produced by damp also remain unchanged. Colors with a metallic or earthy base remain unaltered, while vegetable pigments are entirely removed.

In order to perform the experiment, take a capacious glass flask with a wide neck, introduce a piece of phosphorus three inches in length and half an inch in diameter, pour water heated to eighty-five degreas Fahrenheit into the flask until the phosphorus is half covered, close the flask loosely with a cork, and let it stand in a moderately cool place for twelve or eighteen hours. It will then be filled with ozone. When the water has been poured on the phosphorus, the papers to bo bleached are rolled up, fastened to a platinum wire, moistened, and hung up in the flask. It will soon be noticed that the paper is surrounded by a column of a white smoke which arises from the phosphorus, and the stains will disappear gradually, the time varying from one to three days, according to their nature. Prints which had become brown in age, or were soiled with coffee, became pure and white after one day's treatment.

When the spots have disappeared, the paper yields, an acid reaction consequently, if it were dried aa once, it would not only become brittle, but would again darken. In order to obviate this, the acid must be removed, which is done by first rinsing the paper with pure water until blue litmus-paper is only slightly reddened, then passing it through water to which a few drops of a soda solution have been added, and finally spreading it on inclined glass plates, upon which it thin stream of water is allowed to flow. When litmus remains unaltered by the water running from the glass, the paper may be allowned to dry, and pressing it between sheets of blotting paper till restore its smoothness. It is evident that the process described is not applicable on a large scale, but it certainly requires but little ingenuity to modify it. Neither will it restore darkened oil-paintings. It is true that they get somewhat brighter, but they nevertheless remain dull, and often become stained, probably because the action does not take place uniformly.

It has, however, been ascertained that oxygenized water is well adapted for clearing up picture. This is a compound of hydrogen and oxygen, containing twice as much of the latter as of the former. The surplus is set free by simple contact with various metals and metallic oxides, and acts very powerfully. The darkening of oil-paintings results from the white lead, or other lead compounds which have been used, being converted into do black sulphide of lead by the absorption of sulphureted hydrogen from the atmosphere. If such a painting is washed over with a solution of two parts or oxygenized water in one hundred parts of spring water, the black sulphide of lead is converted into the white sulphate of lead, and thus the former appearance of the painting is regained.